When they find someone better?

Yes, it's normal to be jealous of a friend. I feel that a lot. You're jealous because you can't do the things that he does with his new friends. Maybe you could leave a message to him, even simple ones (such as good morning, etc) just to let him know that you're still around if he needs you. Then maybe after a while, he might realize that he hasnt given you the attention you deserve and talk to you again. Anyway, dont be too pushy, and let him meet new friends while still being his true friend, who's ready to help when there's no one to be by his side.